gistfile1.txt

ENVIRONMENT VARIABLES
       The   behavior  of  grep  is  affected  by  the  following  environment
       variables.

       The locale for category LC_foo is  specified  by  examining  the  three
       environment  variables  LC_ALL, LC_foo, LANG, in that order.  The first
       of these variables that is set specifies the locale.  For  example,  if
       LC_ALL  is not set, but LC_MESSAGES is set to pt_BR, then the Brazilian
       Portuguese locale is used for the LC_MESSAGES category.  The  C  locale
       is  used  if none of these environment variables are set, if the locale
       catalog is not installed, or if grep was  not  compiled  with  national
       language support (NLS).